The invention provides a three-in-one washing kettle for preparing chlorinated polyethylene, and belongs to the technical field of chemical equipment. The three-in-one washing kettle comprises a tank body, a heating coiled tube and a stirring device, wherein the tank body is wrapped by a heat-preservation layer; a high-temperature and corrosion-resisting layer is arranged on the inner wall of the tank body; a filter is arranged in the position, 1/6-1/4 away from the bottom of the tank body, of the tank body; the heating coiled tube is communicated with the top of the tank body and extends into the tank body; the stirring device comprises a stirring motor arranged outside the tank body, stirring blades arranged inside the tank body, and a rotating shaft connected with both the stirring motor and the stirring blades; surface layers of the heating coiled tube, the rotating shaft and the stirring blades are coated with a high-temperature and corrosion-resisting layer. By adopting the three-in-one washing kettle, three steps of deacidification, neutralization and dealkalization in the deacidification process can be integrated in sequence in the chlorinated polyethylene preparation process, the production equipment and the maintenance cost can be reduced, the material transferring time can be shortened, the production period can be shortened, the production efficiency can be improved, heat can be rapidly conducted, the thermal energy utilization rate is high, and the production energy consumption is low.